[PATCH v4] staging: pi433: add debugfs interface

[Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>]

This adds debugfs interface that can be used for debugging possible
hardware/software issues.

It currently exposes the following debugfs entries for each SPI device
probed:

  /sys/kernel/debug/pi433/<DEVICE>/regs
  ...

The 'regs' file contains all rf69 uC registers values that are useful
for troubleshooting misconfigurations between 2 devices. It contains one
register per line so it should be easy to use normal filtering tools to
find the registers of interest if needed.

Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
---
Changelog:

v4: remove unnecessary variable initializer, ensure mutex locks are
	released before returning from routine. Req: Dan Carpenter
v3: fix build error, remove redundant comments and validate return values
        from wait_event_interruptible routines: Req: Greg K-h, Dan Carpenter
v2: remove redudant references to dentry pointers in the code and perform
     debugsfs_lookup instead. Req: Greg k-h
v1: https://lore.kernel.org/lkml/20220123073855.GA79453@mail.google.com/
---
 drivers/staging/pi433/pi433_if.c | 76 ++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
index 86ad497417f7..4fbac3ccef74 100644
--- a/drivers/staging/pi433/pi433_if.c
+++ b/drivers/staging/pi433/pi433_if.c
@@ -41,6 +41,8 @@
 #ifdef CONFIG_COMPAT
 #include <linux/compat.h>
 #endif
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
 
 #include "pi433_if.h"
 #include "rf69.h"
@@ -1098,12 +1100,76 @@ static const struct file_operations pi433_fops = {
 	.llseek =	no_llseek,
 };
 
+static int pi433_debugfs_regs_show(struct seq_file *m, void *p)
+{
+	struct pi433_device *dev;
+	u8 reg_data[114];
+	int i;
+	char *fmt = "0x%02x, 0x%02x\n";
+	int ret;
+
+	dev = m->private;
+
+	mutex_lock(&dev->tx_fifo_lock);
+	mutex_lock(&dev->rx_lock);
+
+	// wait for on-going operations to finish
+	ret = wait_event_interruptible(dev->rx_wait_queue, !dev->tx_active);
+	if (ret)
+		goto out_unlock;
+
+	ret = wait_event_interruptible(dev->tx_wait_queue, !dev->rx_active);
+	if (ret)
+		goto out_unlock;
+
+	// skip FIFO register (0x0) otherwise this can affect some of uC ops
+	for (i = 1; i < 0x50; i++)
+		reg_data[i] = rf69_read_reg(dev->spi, i);
+
+	reg_data[REG_TESTLNA] = rf69_read_reg(dev->spi, REG_TESTLNA);
+	reg_data[REG_TESTPA1] = rf69_read_reg(dev->spi, REG_TESTPA1);
+	reg_data[REG_TESTPA2] = rf69_read_reg(dev->spi, REG_TESTPA2);
+	reg_data[REG_TESTDAGC] = rf69_read_reg(dev->spi, REG_TESTDAGC);
+	reg_data[REG_TESTAFC] = rf69_read_reg(dev->spi, REG_TESTAFC);
+
+	seq_puts(m, "# reg, val\n");
+
+	for (i = 1; i < 0x50; i++)
+		seq_printf(m, fmt, i, reg_data[i]);
+
+	seq_printf(m, fmt, REG_TESTLNA, reg_data[REG_TESTLNA]);
+	seq_printf(m, fmt, REG_TESTPA1, reg_data[REG_TESTPA1]);
+	seq_printf(m, fmt, REG_TESTPA2, reg_data[REG_TESTPA2]);
+	seq_printf(m, fmt, REG_TESTDAGC, reg_data[REG_TESTDAGC]);
+	seq_printf(m, fmt, REG_TESTAFC, reg_data[REG_TESTAFC]);
+
+out_unlock:
+	mutex_unlock(&dev->rx_lock);
+	mutex_unlock(&dev->tx_fifo_lock);
+
+	return ret;
+}
+
+static int pi433_debugfs_regs_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, pi433_debugfs_regs_show, inode->i_private);
+}
+
+static const struct file_operations debugfs_fops = {
+	.llseek =	seq_lseek,
+	.open =		pi433_debugfs_regs_open,
+	.owner =	THIS_MODULE,
+	.read =		seq_read,
+	.release =	single_release
+};
+
 /*-------------------------------------------------------------------------*/
 
 static int pi433_probe(struct spi_device *spi)
 {
 	struct pi433_device	*device;
 	int			retval;
+	struct dentry		*entry;
 
 	/* setup spi parameters */
 	spi->mode = 0x00;
@@ -1252,6 +1318,10 @@ static int pi433_probe(struct spi_device *spi)
 	/* spi setup */
 	spi_set_drvdata(spi, device);
 
+	entry = debugfs_create_dir(dev_name(device->dev),
+				   debugfs_lookup(KBUILD_MODNAME, NULL));
+	debugfs_create_file("regs", 0400, entry, device, &debugfs_fops);
+
 	return 0;
 
 del_cdev:
@@ -1275,6 +1345,9 @@ static int pi433_probe(struct spi_device *spi)
 static int pi433_remove(struct spi_device *spi)
 {
 	struct pi433_device	*device = spi_get_drvdata(spi);
+	struct dentry *mod_entry = debugfs_lookup(KBUILD_MODNAME, NULL);
+
+	debugfs_remove(debugfs_lookup(dev_name(device->dev), mod_entry));
 
 	/* free GPIOs */
 	free_gpio(device);
@@ -1349,6 +1422,8 @@ static int __init pi433_init(void)
 		return PTR_ERR(pi433_class);
 	}
 
+	debugfs_create_dir(KBUILD_MODNAME, NULL);
+
 	status = spi_register_driver(&pi433_spi_driver);
 	if (status < 0) {
 		class_destroy(pi433_class);
@@ -1366,6 +1441,7 @@ static void __exit pi433_exit(void)
 	spi_unregister_driver(&pi433_spi_driver);
 	class_destroy(pi433_class);
 	unregister_chrdev(MAJOR(pi433_dev), pi433_spi_driver.driver.name);
+	debugfs_remove_recursive(debugfs_lookup(KBUILD_MODNAME, NULL));
 }
 module_exit(pi433_exit);
 
-- 
2.34.1